It is known to use robots for assisting and performing surgery. Surgical robots normally consist of a base, an arm, and an instrument. The base supports the robot, and is itself attached rigidly to, for example, the operating theatre floor, the operating theatre ceiling or a trolley. The arm extends between the base and the instrument. The arm typically has a plurality of articulations, which are used to locate the surgical instrument in a desired location relative to the patient. The surgical instrument is attached to the distal end of the robot arm. The surgical instrument penetrates the body of the patient at a port so as to access the surgical site.
FIG. 1 illustrates a typical surgical instrument 100 for performing robotic laparoscopic surgery. The surgical instrument comprises a base 101 by which the surgical instrument connects to the robot arm. A shaft 102 extends between base 101 and articulation 103. Articulation 103 terminates in an end effector 104. In FIG. 1, a pair of serrated jaws are illustrated as the end effector 104. The articulation 103 permits the end effector 104 to move relative to the shaft 102. It is desirable for at least two degrees of freedom to be provided to the motion of the end effector 104 by means of the articulation.
FIG. 2 illustrates an example of a known cabling arrangement 200 in a surgical instrument for transferring drive from the base of the surgical instrument 101 through the shaft 102 to the articulation 103. Cable pair C1, C2 terminate in the articulation as a loop around capstan 202. They then pass as a pair around one side of capstan 201. From there, the cable pair C1, C2 passes over capstan 204 and down through shaft 102 to the base of the instrument 101. Cable pair C3, C4 terminate in the articulation as a loop around capstan 203. They then pass as a pair around the other side of capstan 201 to C1, C2. From there, the cable pair C3, C4 passes under capstan 204 and down through shaft 102 to the base of the instrument 101.
Rotation of yoke 205 about capstan 204 causes the articulation 103 and hence the end effector 104 to pitch about the capstan 204. Pitching in one direction is enabled by pulling cable pair C1, C2 and releasing cable pair C3, C4. Pitching in the other direction is enabled by pulling cable pair C3, C4 and releasing cable pair C1, C2. Rotation of capstan 202 causes one jaw of end effector 104 to move. Movement in one direction is enabled by pulling cable C1 and releasing cable C2. Movement in the other direction is enabled by pulling cable C2 and releasing cable C1. Rotation of capstan 203 causes the other jaw of end effector 104 to move. Movement in one direction is enabled by pulling cable C3 and releasing cable C4. Movement in the other direction is enabled by pulling cable C4 and releasing cable C3. Cables C1, C2, C3 and C4 are driven individually and independently by drivers D1, D2, D3 and D4 respectively.
In the context of minimally invasive surgery, it is desirable to reduce the external diameter of the shaft in order to minimise the size of the incision through the skin of the patient and disruption inside the patient's body. It is also desirable to minimise the weight of the surgical instrument so as to minimise the size and weight of the robot base and arm required to support the instrument, thereby enabling the robot as a whole to be more moveable within the operating theatre.
It would therefore be desirable to reduce the size and weight of the driving mechanism in the surgical instrument whilst retaining the ability to articulate the end effector as described above.